The purpose of the proposed research is to increase our knowledge of the functional role of peripheral vascular afferents in the neural control of circulation. This work will focus on the venous afferent mechanoreceptive properties and reflex connections to skeletal muscle motoneurons. This proposal is based on the long-standing anatomical description of vascular afferents and receptors in the walls of peripheral blood vessels; on previous reports of veni-vasomotor reflexes; and on the previous work by the applicant on femoral venous afferent electrophysiology. The mechanical response properties of femoral venous afferents are being studied by analysis of saphenous nerve single fiber responses to static and dynamic distentions of a segment of femoral vein (at the origin of the saphenous vein). Femoral venous afferent connections to spinal cord neurons are being mapped by laminar and single unit analysis of activated neurons, reflex condition-test analysis, and intracellular recordings from motoneurons. Patterns of skeletal muscle activation by electrical and mechanical activation of femoral venous afferents will be examined by analysis of EMG activity in several hindlimb muscles. The results of the proposed work will provide a substantial basis for establishing reflex elicited skeletal "muscle pumping", and greatly extend consideration of the peripheral vasculature afferents in the neural control of circulation.